Immunological identity is traditionally defined by genetically encoded antigens, with equal maternal and paternal contributions as a result of Mendelian inheritance. However, vertically transferred maternal cells also persist in individuals at very low levels throughout postnatal development. Reciprocally, mothers are seeded during pregnancy with genetically foreign fetal cells that persist long after parturition. Recent findings suggest that these microchimeric cells expressing non-inherited, familially relevant antigenic traits are not accidental 'souvenirs' of pregnancy, but are purposefully retained within mothers and their offspring to promote genetic fitness by improving the outcome of future pregnancies. In this Review, we discuss the immunological implications, benefits and potential consequences of individuals being constitutively chimeric with a biologically active 'microchiome' of genetically foreign cells.

传统上，免疫学特性是由基因编码的抗原定义的，由于孟德尔遗传，母体和父体的贡献相等。然而，垂直转移的母体细胞在整个出生后发育过程中也以非常低的水平持续存在于个体中。相反，母亲在怀孕期间被植入具有遗传性的外来胎儿细胞，这些细胞在分娩后仍会持续很长时间。最近的研究结果表明，这些表达非遗传性、家族相关抗原特征的微嵌合细胞并不是偶然的怀孕“纪念品”，而是有意保留在母亲及其后代体内，通过改善未来怀孕的结果来促进遗传健康。在这篇综述中，我们讨论了个体与遗传外来细胞的生物活性“微基因组”进行组成型嵌合的免疫学意义、益处和潜在后果。